The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
This disclosure relates to a method and system for reading data that has been recorded in an arrangement of tracks on a storage medium and is read by a read head that moves relative to the surface of the storage medium. More particularly, this disclosure relates to compensating for a track squeeze condition resulting from one or more off-track conditions during the writing of an adjacent track or tracks.
In magnetic recording, as one example of a type of recording in which reading and writing are performed by a head that moves relative to the surface of the storage medium, data may be written in circular tracks on a magnetic disk. To write data on a given track, the write head may be centered on that particular track. However, sometimes the write head may deviate from its ideal path and stray “off-track,” with part of the head over the current track (i.e., the track to be written) and part of the head over an adjacent track. This results in a portion of the data that may have been written previously on the adjacent track being overwritten. Later, when what had been the adjacent track is the current track to be read, and what had been the current track is now the adjacent track to the track to be read. At that time, the signal that is read from the now-current track may include inter-track interference (“ITI”) from the now-adjacent track. Moreover, if the track on the other side of the now-current track also had been written after the now-current track was written and also experienced an off-track condition during that write operation, the signal from the now-current track may also include ITI from the other adjacent track, making it even more difficult to read. The encroachment on the current track from the adjacent tracks on either side of the current track gives rise to a condition that may be referred to as “track squeeze.”
If an ITI-generating event on a particular current track resulting from an off-track condition during writing of an adjacent track is detected before the adjacent track is written again, then it may be possible to recover the data on the particular current track by using ITI cancellation, such as the ITI cancellation technique disclosed in copending, commonly-assigned U.S. patent application Ser. No. 12/882,802, filed Sep. 15, 2010 and hereby incorporated by reference herein in its entirety. However, many times it is the case that a particular track will have been “squeezed” by multiple ITI events on its adjacent tracks before an attempt is made to read that particular track. In such a case, ITI cancellation techniques such as those described may not be useful, because the current data on the adjacent tracks may not be the data causing interference on the current track, but rather the data causing the interference may have been overwritten in the interim and at most only unusable remnants of those data may remain.